1. Field of the Invention
The present invention relates to a communication system, and more particularly to an apparatus and method for re-transmitting erroneous packet data on a physical layer of the communication system.
2. Background of the Related Art
A system that is used for data communications between open system interconnections (OSIs), is divided into 7 layers in terms of functional commonality and independence. For respective layers, necessary protocols are stipulated. In most current wire and wireless communication systems, seven such OSI Layers are referenced.
The seven OSI Layers include a physical layer (Layer 1), a data link layer (Layer 2), a network layer (Layer 3), a transport layer (Layer 4), a session layer (Layer 5), a presentation layer (Layer 6), and an application layer (Layer 7).
Generally, transmission data is generated at an upper layer, for example, Layer 7, Layer 6, Layer 5, or Layer 4. This data is then applied to a lowermost layer via intermediate layers. The transmission data from the lowermost layer is then transmitted to the lowermost layer of the counterpart via a physical medium, for example, a line, so that it is finally transmitted to a desired intermediate or upper layer.
Re-transmission of erroneous data is typically carried out at the data link layer (Layer 2) or the transport layer (Layer 4).
The re-transmission at the data link layer (Layer 2) is achieved using a Go-Back-N method or a Selective-Repeat method. The Go-Back-N method is a method in which the transmission data is re-transmitted in response to a negative acknowledgment (NAK) signal indicative of an error in the transmission data. On the other hand, in accordance with the Selective-Repeat method, only the erroneous data is re-transmitted.
The re-transmission at the transport layer (Layer 4) is typically achieved using TCP/IP. In accordance with this method, if there is no acknowledgment (ACK) signal from the reception end to indicate a normal reception of 8-Kbyte data, the 8-Kbyte data is re-transmitted from the transmission-end TCP/IP (Layer 4).
A system for transmitting packet data may be either a circuit mode or a packet mode in accordance with the type of transmission data. In the circuit mode system, a path is set between a transmission node and a reception node so that the path is exclusively used until the connection between the transmission and reception nodes is cut off.
In accordance with the packet mode system, data is transmitted in the form of packets, each having a desired length. Accordingly, one line can be simultaneously used by a plurality of terminals without being exclusively used by one terminal. In the packet mode system, it is necessary to use overhead data, indicative of the destination of data and the start and end of data, for every packet. The data transmission time is increased by the overhead prefixed to each packet. The same problem is involved when data must be re-transmitted due to the generation of errors in the packet data.
FIG. 1 is a block diagram illustrating a related art procedure for re-transmitting erroneous packet data. Respective general functions of layers illustrated in FIG. 1 will now be described.
Transport layers 10 and 15 (Layer 4) manage the quality of the communication network for transmission of data. Each of the network layers (Layer 3) (not shown) executes a desired routine using the communication network, and sets a connection to the counterpart system. Data link layers 20 and 25 (Layer 2) establish line links, detect transmission errors, and recover those transmission errors. Physical layers 30 and 35 (Layer 1) control electrical and mechanical conditions to allow a physical connection of lines, and a maintenance and cut-off of that physical connection. The physical medium 40 is typically a wire or wireless transmission line for transmitting data signals received from the physical layers 30 and 35. In FIG. 1, the network layers are not shown for the convenience of illustration. Also, the transport layers are denoted by “TCP/IP”.
The related art re-transmission method for erroneous packet data will now be described in conjunction with FIG. 1.
The transmission-end terminal (base station) of a WLL system generates data at its upper layer, and applies the generated data to Layer 1 30 via Layer 2 20. The data from Layer 1 30 is transmitted to Layer 1 35 of the reception-end terminal, and then sent to the upper layer of the reception-end terminal via the layers of the reception-end terminal.
The method for processing errors generated during the above transmission procedure may be varied, depending on the transmission control method used.
In accordance with a Go-Back-N method and a selective-repeat method, re-transmission of data is carried out by the data link layers 20 and 25. When the base station data link layer 20 is informed of the generation of errors from the reception end, it re-transmits associated data stored in its buffer. This data is sent to the reception-end physical layer (Layer 1) 35 via a wireless transmission line via the base station physical layer (Layer 1) 30. The data is finally transmitted to the reception-end data link layer 25.
In accordance with the re-transmission method using TCP/IPs, the transport layers 10 and 15 carry out re-transmission of data. When the transmission-end transport layer 10 is informed of the generation of errors from the reception end, it re-transmits associated data stored in its buffer. This data is then sent to the reception-end physical layer (Layer 1) 35 via Layer 3, Layer 2 20, Layer 1 30, and a wire transmission line. Finally, the data is transmitted to the reception-end transport layer 15 via the reception-end Layer 2 25 and Layer 3.
Packet data, which is transmitted as mentioned above, has overhead data added to it at its leading and trailing ends, respectively. The overhead data added to the leading end of the packet data contains information regarding synchronization and destination address, etc. The overhead data added to the trailing end of the packet data contains information regarding the detection and correction of errors generated during the transmission of data. For example, where data is transmitted for 5 to 107 ms, the leading and trailing overheads take transmission times of 60 ms and 20 ms, respectively. Thus, the time taken to transmit the overheads in the packet mode is substantially equal to the transmission time of associated data.
The related art method of handling erroneous data has various problems. For example, the delay of transmission resulting from the overhead transmission time is importantly treated in the Go-Back-N method and the TCP/IP re-transmission method inevitably involving the re-transmission of a frame with a certain size or at a certain interval, as compared to the selective repeat method adapted to re-transmit only a particular frame involving errors.
Furthermore, the re-transmission of data is delayed until the erroneous data reaches the upper layer because it is carried and requested out by the upper layer. For this reason, loss of time is inevitably involved.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.